Freelance writer Cam Cheung Wai-nui and her husband, former police superintendent Robert Highfield, are unconventional parents. When the couple decided after Highfield's retirement in 2005 to realise his childhood dream of sailing around the world, they surprised friends and relatives by taking their two young daughters along.

During the voyage Molly and Nancy, now aged 13 and 11, kept up with their studies through a home-schooling programme. When they returned from the odyssey in 2009, the usual school classrooms awaited them.

But while others might send their children to elite schools and enrol them in special interest classes to bolster resumes, their parents sent them to an integrated government school with a programme for special needs pupils.

The idea, Cheung says, was to give the girls some early exposure to people from different backgrounds by having them study alongside hearing-impaired, autistic and hyperactive children.

But after the freedom and flexibilty of home-schooling, Hong Kong's regimented education proved too much for their daughters. So, after Easter this year, just months before Nancy was due to complete her primary education, Cheung took them out of the school and went back to teaching the girls herself.

Cheung has since written a book about her experiences in devising a home-schooling curriculum and the insight she gained from delving into various education issues. Titled My Children Learn Differently (Feel Publishing), the Chinese-language title, released last week, is also a biting critique of the local education system.

Two years on the treadmill of Hong Kong classrooms turned her daughters from lively youngsters into a couple of lost, listless girls, Cheung says.

'They no longer had [their own] views on things,' she says. 'I asked them many questions [about their day] but they just shrugged and present an impassive face.'

Cheung blames the school's exhausting study schedule for dampening her children's enthusiasm and curiosity about the world around them.

'When we home-schooled them during our four-year trip, it was very flexible. All homework was during class time, which we set at three hours a day. They had free time after classes. After living like that for four or five years, they found local school life strange.

'Molly had to spend several hours every day completing her homework, and this caused her a severe lack of sleep. The homework, which required copying and model answers, was very monotonous. They were so tired after school that I had to cut down on visits to grandparents and other activities,' Cheung recalls.

Although deeply disenchanted with the local education system, Cheung says she and her husband struggled with the decision to resume home-schooling.

'After four years of home-schooling them at sea, I was eager to hand back the responsibility of teaching them to the school. A sentence uttered by a teacher is more powerful than thousands of words from a mother. Deadlines also work better in a school setting, as teachers are more authoritative and they get a different kind of respect from children,' she says.

'Moreover, I was chairwoman of the parent-teacher association at Wo Che Lutheran School in Sha Tin which Nancy was attending. She was only several months away from graduating when she left. The school showed genuine care about students' learning needs and I felt I was deserting it.'

But this was outweighed by the Highfields' concerns about the effect that the straitjacket-learning system in government schools was having on their children, especially Nancy.

Their elder daughter, Molly, had adapted better. She got on well with her classmates in primary school and did well enough to secure a place in Pui Ying College, a sought-after secondary school in Sha Tin.

But Nancy, who loves art and wants to become an artist, didn't enjoy her time back at school at all.

'All the kids would only talk about their favourite anime characters and other silly things,' she says.

'I could not find a way to communicate with them without saying something that made them think I was weird. The classes were so boring that you almost fall asleep.'

Cheung says their younger daughter enjoyed life on the boat when both parents were around all the time.

'She doesn't like it when I am not at home. The pressure of school made it worse,' says Cheung. 'She has very strong views on things and her forgetfulness sometimes got her into trouble at school. She found most of her classmates immature, couldn't make many friends and would take a novel to school and read alone in a corner most of the time.'

Cheung criticises officials for creating an education system that emphasises homework and academic learning at the expense of students' overall development. It even encroaches on precious family time, which mostly revolves around discussions about revisions and exams.

Instead of helping children to be self-learners who can find out answers by themselves, she says teachers here expect conformity from students who are simply fed chunks of facts.

History textbooks in Hong Kong are mostly filled with dry facts compared with the well-written course material for the US-devised Calvert school curriculum, which she chose for home-schooling at sea. The components about Greek mythology and art history are written in such a lively way that I enjoy reading them too,' Cheung says. 'While local students have to copy their composition with all the teachers' corrections, Calvert gives students a free rein with writing exercises. Parents highlight the mistakes, so their work isn't filled with big crosses.'

It took nerve, resolve and hard work for the Highfields to push ahead with home-schooling in Hong Kong, not least because parents are required by law to send their children to school.

'A proposal for home-schooling is scary in Hong Kong, where it's illegal to keep children away from school. We wrote to the Education Bureau setting out our plan and spelling out our justifications for doing so,' Cheung says.

As might be expected, the Highfields' scheme met with a cool reception. The Education Bureau replied saying that students were required by law to attend a recognised school, Cheung recalls, and officials made inquiries at their daughters' school and asked the principal to have a word with them.

But the couple persisted in their quest. They met Education Bureau officials in their Kowloon Tong headquarters and presented detailed plans.

Their thorough groundwork evidently won over the officials: 'In the end, they acknowledged that some children benefited from alternative education although they stressed that the policy is for youngsters to be educated in schools. They eventually approved [our application] and they will conduct a home visit to see our progress later.'

Cheung reckons her biggest challenge is working out how to instil self-discipline in her daughters and how to make learning interesting for them.

'Home-schooling is a big learning process for me. I have been reading books on how to teach critical thinking, classroom management and child psychology. We are still working on the best methods to teach them.'

Highfield takes an active role in the girls' education: besides drawing up the lesson schedule, he is responsible for teaching history and geography.

'Most kids hate history. They have to memorise a lot of meaningless facts. I am taking them this year through the history of the human race from its beginning up to the civilisations and peoples in the world today. When doing this, we also cover the geography of mankind's spread and where they ended up and why. They are learning about the principles of palaeoanthropology and DNA studies which will give them a good foundation for more detailed study later.

'Once they understand the general picture of the whole of human history, we will go into more detail in chosen areas that interest them.'

Chinese language is his wife's sole purview, but he also supports her in maths, science and English lessons.

'[The girls] usually won't mess around. If they get bored, we do something different,' Highfield says. 'Most of the time, Cam is the disciplinarian and I am the cajoler to get them to toe the line. I usually inject humour, which helps if things are not going well.'

Cheung also goes out of her way to develop interesting educational material for her daughters. Sam Hui Koon-kit's Canto-pop classics, for instance, can offer insight into Hong Kong's social and cultural changes.

'I try to use current affairs and things relating to daily life when teaching Chinese. They love the political satire in Civic Party legislator Tanya Chan Suk-chong 's recent stand-up show,' she says.

The girls may return to conventional classes when they advance to higher levels, but, for now, their parents haven't set a timeline for the home-schooling.

'It all depends on how they are doing,' Cheung says.

To make up for the loss of their seafaring lifestyle when they returned to Hong Kong, she enrolled her daughters in dinghy sailing classes, and Molly has taken to the sport with gusto.

'Sailing practice continues under the sun or rain. By exposing them to the elements and getting them to use skills and speed to beat others, the sport can train their perseverance and all-round development,' she says.

'My husband tried teaching them sailing while we were in Vanuatu, but they didn't pick it up until they came back to Hong Kong. Molly really loves boat racing and wants to be a professional sailor after she grows up.'

With Highfield and Cheung closely involved in their children's education, learning is a collaborative activity that often involves everyone in the family.

'We devote six hours every day to learning. There's no homework. We do outings and physical education together. We play badminton and go swimming. I sometimes do crafts, cooking and knitting with them for home-economics lessons. Learning is far more efficient when the subject matter is interesting and they are not in a big class with pupils of varying ability,' says Cheung.

'Molly has just finished writing her second novel and is working with her dad on a book on poems. When they finish, Nancy will provide the illustrations and I will do the Chinese translation.'